1. Field of the Invention
The present invention relates to a cam profile data creation apparatus and a synchronization controller, and particularly to a technique for adjusting an error between an operation of a driven shaft defined in cam profile data and an actual instruction operation for the driven shaft.
2. Description of the Related Art
Conventionally, electronic cams for electrically realizing similar operations to mechanical cams have been used. In order to control such electronic cams, at first, a cam profile data creation apparatus previously defines a table (hereinafter referred to as cam profile data) defining a correspondence relationship between a phase of a drive shaft and a displacement of a driven shaft. A synchronization controller then finds a displacement of the driven shaft synchronized with a phase of the drive shaft based on the cam profile data thereby to position the driven shaft. Thereby, operations equivalent to those of a mechanical cam having a certain profile can be electrically reproduced.
In such electronic cam control, a definition point, which is not used for positioning when a rotation speed of the drive shaft is increased, (which is paired data of a phase of the drive shaft and a displacement of the driven shaft, included in the cam profile data) may occur. A phase of the drive shaft is generally designed at a certain interval of θ0 in the cam profile data. Herein, a cycle (hereinafter referred to as control cycle) in which the synchronization controller actually performs an instruction operation on the driven shaft is assumed as τ. The amount of change in phase of the drive shaft per control cycle τ is assumed as phase interval θ. The phase interval θ is determined depending on a rotation speed of the drive shaft.
As illustrated in FIG. 8A, when a phase interval θ0 of the drive shaft defined in the cam profile data matches with the actual phase interval θ of the drive shaft, each definition point is absolutely instructed and the electronic cam operates as assumed when the cam profile data is created. On the other hand, when a rotation speed of the drive shaft is faster and the phase interval θ is larger than the phase interval θ0 of the drive shaft in the cam profile data, a definition point that is not instructed is caused. An actual operation of the driven shaft in this case may be as illustrated in a solid line in the graph of FIG. 8B. Thereby, an error is caused between an operation of the driven shaft defined in the cam profile data and an actual instruction operation for the driven shaft, and there occurs a problem that the electronic cam cannot produce a maximum stroke, for example. The error easily occurs particularly where a change in displacement is large.
Conventionally, the synchronization controller actually performs an instruction operation on the driven shaft to operate the electronic cam, confirms a positional deviation at this time, or an error between an actual displacement of the driven shaft and a displacement of the driven shaft defined in the cam profile data, and further carries out control for compensating the error, thereby solving the above problem. For example, Japanese Patent Application Laid-Open No. 07-104855 discloses an electronic cam control method for controlling a servo system in response to a position instruction, wherein if a phase delay due to a follow-up delay of a servo system with respect to a position instruction is caused, the phase delay is compensated by first issuing a position instruction in consideration of the phase delay.
According to the technique described in Japanese Patent Application Laid-Open No. 07-104855, mentioned above, the controller actually operates a machine to confirm a positional deviation. With such a method for making confirmation by actually operating a machine, however, the machine may sometimes erroneously operate, which is not preferable in terms of safety. Further, an instruction operation of an electronic cam is determined depending on a relationship between cam profile data and a rotation speed of the drive shaft, but in adjustment where a machine is actually operated, there is no method for visually confirming such relationship, as a result, the confirmation has to be made by trial and error, which will be a burdensome task. Therefore, it is desirable to confirm, before the machine is actually operated, the situation of generation of an error between an actual instruction operation for the driven shaft in a specified rotation speed of the drive shaft and definition points defined in cam profile data.